$ssh2->check_hostkey(LIBSSH2_HOSTKEY_POLICY_ASK);
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Hi, I don't want to feel like a dufus, but I tried

my $return = $ssh2->check_hostkey(LIBSSH2_HOSTKEY_POLICY_ASK);
print "Return:  $return\n\n\n\n";
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and all I get is Return 00 and the normal filehandle printout. How exactly do I efficiently print out the returns from the check_hostkey command.? I'm cultivating laziness. :-)

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I'm not really a human, but I play one on earth. ..... an animated JAPH

If the remote host key is good enough for the given policy, the method returns a true value. Otherwise it returns undef and the error (or die_with_error) method can be used to find out the failure cause.

$ssh2->check_hostkey(LIBSSH2_HOSTKEY_POLICY_ASK)
    or $ssh2->die_with_error;
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The 0-but-true value 00 is equal to LIBSSH2_KNOWNHOST_CHECK_MATCH.

Thanks for this post, zentara, it's really helped me understand the concepts and implementation of rsa authentication in perl. I think that I achieve success in that an sftp object is created using key pairs. The very critical thing to first do is this:

$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/bob/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/bob/.ssh/id_rsa.
Your public key has been saved in /home/bob/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:LCWI8Wrw14m0Cxz1P+TqmL7Nn+mY19fWETCfjYK87VY bob@bob-ThinkPad-SL
+510
The key's randomart image is:
+---[RSA 2048]----+
|  . .   .        |
|   = o o     o   |
|. o + o +. .  +.o|
| + + + B .o . .+.|
|  * + = S  o .  .|
| . o = .  . . E. |
|    + .  . . o ..|
|   . o o.o. + o .|
|    o.=+=  o .   |
+----[SHA256]-----+
$
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This was output upon first running:

values are home349337426.1and1-data.host 
The authenticity of host 'home349337426.1and1-data.host' can't be esta
+blished.
Key fingerprint is SHA1:6bfe32c8859a967c8ed6cebdd5c48b72edff71c7.
Are you sure you want to continue connecting (yes/no)? y
mkdir is not a valid Net::SSH2 macro at ssh4.pl line 31.
$ 

$
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Running it again, I get none of the dialog regarding whether the responder is trusted. At the end, I'm still left with not being able to invoke a mkdir method.

Turning to the source, the meaning for password has shifted from the one you use for login to the one you used to create the ciphers.

#!/usr/bin/perl -w
use strict;
use Net::SSH2 qw(LIBSSH2_CHANNEL_EXTENDED_DATA_MERGE
                        LIBSSH2_CHANNEL_FLUSH_ALL
                        LIBSSH2_HOSTKEY_POLICY_ASK);

use 5.010;
use lib "template_stuff";
use config2;

# none of this makes any sense until you run
# ssh-keygen -t rsa

my $sub_hash = "my_sftp";
my $domain = $config{$sub_hash}->{'domain'};
my $username = $config{$sub_hash}->{'username'};

say "values are $domain";
my $pass = "ringo";
my $ssh2 = Net::SSH2->new( debug => 1 ); 
$ssh2->trace(-1);
$ssh2->timeout(5000);

$ssh2->connect($domain) or $ssh2->die_with_error;
$ssh2->check_hostkey(LIBSSH2_HOSTKEY_POLICY_ASK);

$ssh2->auth_publickey($username,
                 '/home/bob/.ssh/id_rsa.pub',
                   '/home/bob/.ssh/id_rsa',
                $pass );

my $success = $ssh2->mkdir("perlmonks");
say "success is $success";
return 0;

__END__
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I return to the documentation to find that sftp methods are less than fully supported, indeed that I'm advised to use something else: https://metacpan.org/pod/Net::SSH2#sftp I have found it immensely instructive so far, even if I might use the higher level Net::SFTP::Foreign henceforth. I hope to be able to do roughly this same exercise with that module.

the meaning for password has shifted from the one you use for login to the one you used to create the ciphers

Exactly!! :-) Glad you are figuring it out.

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I'm not really a human, but I play one on earth. ..... an animated JAPH